I presume that you already know how to scrub along the timeline dragging the top of the playback marker by holding down the left mouse button and that you want to also hear the audio. If so, right-click on the speaker button at the top right of the Project Window and select Scrubbing 1 frame or long.
Actually I have been using MEP for about 10 years now and have made over 400 short video projects.
Some years ago I started using my mouse to be able to scrub along the timeline as an alternative to the suggestions you have both made and other keyboard shortcuts. Although uncertain if I actually changed any settings or it is a default for the mouse as unfortunately I cannot check this on my PC.
When using the mouse to scrub I am able to do it without taking my hand off the mouse which saves me a lot off movements and of course taking my eye from the screen to the keyboard each time is a benefit.
Firstly I use the left mouse button to stop at a point along the timeline to check a transition etc. Then I press the scroll wheel which starts the playback from that point. To stop the playback I press the scroll wheel again which takes the playback marker back to my original position. Just press again to restart the playback. As the playback marker moves along the timeline if I want to change the start position I press the left mouse button and it scrubs from that position.
I hope this explains my question.
Just wondering if you would be kind enough next time you open MEP to try and use the mouse this way just in case it is a default setting.
Now I understand. So long as the mouse wheel can be pressed, it still works. Try pressing and holding the mouse wheel in for a fraction of a second longer. Just a quick press does not start playback.